Method of bonding powdered



March 2, 1943. c. E. SWARTZ 22,232

METHOD OF BONDING POWDERED METALLIC MATERIAL Original Filed July 22,1936 ficQZ' ATTORNE- 6" Reissued Mar. 2, 1943 22,282 METHOD or nonnmc.POWDERED METALLIC MATERIAL Carl E. Swartz, Shaker Heights, Ohio,assignor,

by mesne assignments, to S. K. Wellman Company, Cleveland, Ohio, acorporation of Ohio Original No. 2,161,597, dated June 6, 1939, SerialNo. 91,870, July 22, 1936. Application for reissue June 5, 1941, SerialNo. 396,786

4 Claims.

The present invention relates to a novel method for bonding a powderedmetallic material or mixture to a solid supporting body such as steel.

The general object and nature of the invention is to provide such abonding process which will produce an eflicient and satisfactory unionof the powdered material, in sintered form, to the solid material orsteel.

A further object of the invention is to eliminate the formation ofvarious oxides, metallic alloys, and other chemical compounds whichheretofore have weakened and contaminated the bond or juncture betweenthe sintered metallic material and the solid body so that a practicaland commercially adaptable product was not obtainable.

Brieflly outlined, the method embodying the principle of my inventioncomprises the initial step of properly cleaning, both mechanically andchemically, the surface of the supporting steel body, and thenmaintaining such cleaned surface in uncontaminated and protectedcondition while the powdered metallic material, placed in contacttherewith, is heated to a sintering temperature. The term cleaning ashere used means the removal of all particles and films of foreignmaterial from the surface of the steel and the maintaining of thecleaned surface in such a condition during the cleaning operation andimmediately thereafter that it will not again immediately collect suchforeign particles or films by oxidation.

To the accomplishment of the foregoing and related ends, said invention,then, consists of the steps hereinafter fully described and particularlypointed out in the claims, the annexed drawing and the followingdescription setting forth in detail one approved method of carrying outthe invention, such disclosed method however, constituting but one ofthe various'ways in which the principle of the invention may be used.

In said annexed drawing:

Fig. l is a. perspective view of a ringof the solid supporting metalbody such as steel; Fig. is a sectional view of the ring of Fig. 1,showing a layer of the protective material applied to the surface of thering; Fig. 3 is a cross-sectional view of an apparatus illustrating theperformance of the sintering and bonding step of my process; and Fig. 4is a sectional view of the finished product.

The herein described and claimed method is particularly adaptable forthe manufacture of composite metallic elements intended for use whereinthe elements are subjected to rubbing or frictional surface contact.Articles of manufacture fabricated from the composite metallic elementsproduced by my process may take the form of brake linings, clutchfacings, bearings, and the like. The particular article here describedby way of exemplary illustration in the practice of my method is aclutch facing element in the form of a flat ring and consisting of thereinforcing supporting body I of solid metal such as steel with thelayer 6 of sintered metallic powdered material boned thereto.

In the practice of my process, the first step consists of mechanicallyand chemically cleaning the surface of the steel supporting body I. Suchcleaning is effected by any of the customary methods such as grinding,abrading, polishing, machining, sand blasting, pickling, or acombination thereof. After such cleaning of the surface of the steelring I has been accomplished, the surface is covered with a protectivecoating capable of remaining stable at all elevated temperatures. By theterm elevated temperature is meant that temperature at which the bondingis begun between the powdered composition and the steel and also thetemperature at which all of the oxygen entrapped in the powderedmaterial or carried on the surface of the steel or coming from anycompound which would give off oxygen has been dissipated or combined sothat it will not be able to prevent bonding of the material to thesteel. The term protective coating is used herein to refer to a coatingwhich will remain protective up to the temperature referred to as anelevated temperature, which is the temperature at which the bondingbetween the steel and the compound begins, that is, the temperature atwhich all of the oxygen, which might otherwise prevent bonding, has beendissipated or combined. Particularly suitable for the purpose ofsupplying such protective coating is a flash coat of copper plating. Inorder to produce such a flash coating of copper on the surface of thesteel ring I, the latter is placed in an electrolytic deposition bathand allowed to remain at least until there is produced a copper color onthe steel surface.

The protective coating 2 applied to the steel ring I may also consist ofa non-reactive material, such as a high flash point oil, which willremain protective and will not become completely decomposed or gaseousuntil subjected to a. temperature above that herein referred to as anelevated temperature.

The steel ring I with its protective coating 2 is next placed in aforming die, consisting of the femaledie member 4 and the male diemember or plunger 5, with the layer of powdered metallic material 3superimposed on the steel ring I. The assembled elements in theapparatus shown in Fig. 3, consisting of the steel ring I, theprotective coating 2 and the layer of powdered metallic material 3 arethen subjected to pressure and a temperature sufiicient to sinter thepowdered material 3 and to thereby bond the layer to the steel ring I.One method of compressing and sintering the powdered material and thesteel supporting layer is more particularly described and claimed in myco-pending application Method of making composite metallic elements,"filed July 22, 1936, Serial No. 91,- 869 (United States Patent2,156,611)

The resultant product of the above described process is shown in Fig. 4,and consists of the layer of sintered, powdered metallic material 8strongly bonded to the steel layer I along the bonding line 1. Themetallic powdered material 3 may consist of a mixture of a base metalsuch as aluminum or copper with smaller proportions of other materialssuch as tin and lead and also relatively inert material such as powderedsilica, magnesia, talc, graphite or silicon carbide. The use of aprotective coating 2, consisting of a flash coat of copper, isparticularly desirable in the performance of my process where a copperbase metallic powder is used, and almost mandatory in case a high carbonsteel is used. f the relatively inert materials above specified assuitable constituents of the powdered material, graphite is especiallydesirable to be used when a protective coating of copper is employed forthe steel.

The fine particles of the powdered material contain a substantial amountof oxygen and nitrogen in the form of air, some entrained in the mixtureand some contained by surface adhesion on the particles, which ifallowed to come in contact with the cleaned surface of the steel layer Iduring the heating step, will prevent the formation of an eflicient andsatisfactory bond due to chemical reaction of the faces to be bondedwith these gases. Furthermore, the protective coating of copper plating2 prevents any 0! the constituents of the powdered material 3, uch astin, from contacting the surface of the steel layer l and in turnalloying with the iron in the steel, which alloy would also be of abrittle and nonductile nature susceptible of fracture upon flexing 1 ofthe finished composite element. As will be noted from the illustrationof Fig. 4, the layer 2 of copper plating disappears after the heatingand sintering of the powdered material 3, since it is absorbed by thecopper already present in the powdered mixture, leaving the directbonding line 1 between the steel layer 1 and the sintered layer 6.

The provision of the protective coating 2 in the performance of theabove described method, whether it be in the nature of the copperplating, the high flash point oil, or a similar material capable ofremaining stable at an elevated temperature, prevents the entrappedoxygen in the powdered material 3 from coming in contact with thecleaned steel surface during heating and sintering, so that the bondingline is not contaminated and the efiiciency of the bond is notdestroyed.

Other modes of applying the principle of my invention may be employedinstead of the one explained, change being made as regards the processherein disclosed, provided the step or steps stated by the followingclaims or the equivalent of such stated step or steps be employed.

I therefore particularly point out and distinctly claim as my invention:

1. A method of bonding powdered metallic material to a ferrous metalsupport comprising the.

steps of providing a mechanically and chemically clean surface on thesupport, covering such surface with a thin protective coating capable ofprotecting the ferrous metal of the support from oxidation up to anelevated temperature, holding a body of the powdered material having ametal base with a melting point not lower than that of aluminum incontact with the said coating, and effecting substantially completediffusion of the coating and sintering of base metal of the powderedmaterial directly to the ferrous support by suitably heating theassembled support, coating and powdered material, the said coatingserving during the heating to protect the clean surface of the ferroussupport from the action of oxygen in the body of powdered material andthe diffusion of said coating permitting a strong bond resistant to hightemperatures to be formed directly between the ferrous support and thehigh melting point base metal of said body.

A method as claimed in claim 1 comprising the step of covering the cleansurface of the terrou's 1metal support with a protective coating of me a3. A method as claimed in claim 1 comprising the steps of covering theclean surface of the ferrous metal support with a protective coating ofcopper, and effecting substantially complete diffusion of said coatinginto the base metal o"fthe powdered material in the heating of theassembled support, coating and powdered material.

4. A method as claimed in claim 1 comprising the step of covering theclean surface of the ferrous metal support with a protective coating ofhigh flash-point oil.

CARL E. SWAR'I'Z.

